Electrical selector system



July 16, 1935l M. D. SARBEY 2,008,563

ELECTRICAL SELECTOR SYSTEM Filed Dec. 15, 1935 3 Sheets-Sheet 1 f il) Aa.. N.. G L mw J 4 4 m :u u T U a nl mm Ii. a \.,J T., U k J Fa f ...51VAll. C. 'Il v W1 n. Rw w.. Rm m. Rm 1MB k T... c. T: s j. Q .w 6 .z R wC: Il V M. F .AI... ||uH U ma r, 4 .u M :..W n" 4 ...luv H. G -.5 n f. nkw Wm n.. ,mm v r.. 5 2 W A .v m a. F n 1 ||||L .I l I I I -......lllm

M. D. sARBEY ELECTRICAL SELECTOR SYSTEM Filed Dec. 1s, 193s July 16,1935l Hyj- Inventor l /Vnwe/E 3 Sheets-Sheet 2 maynz'ade 0f incwm'nysignal:

l?. E Amplifier l Il il ll'il Al'torney July 16, 1935.

M. D. SARBEY ELECTRICAL SELECTOR SYSTEM 3 Sheets-Sheet 5 Filed Dec. 13,1933 3gp 'W Tfr v v kar :z I .e

Urn: fo calldfubnrter.: or Group:

l Patented July 1.6, 1935 l l t UNITED :STATES PATENT `OFFICE ELECTRICALsELECTon :SYSTEM v Maurice Sarbey, Bay Village, Ohio ApplicationDecember 13, 19st, serial No. 702,267

\ ze claims. (Crus-za) This invention relates to electricalcontrolsysatedl and thosel noty operated, and causing the tems, andparticularly to control systems adapt- Vdevice operated nearest to theline of division to ed to the conveyance of independentv diilerentiput`out of operation all, of the others operated.,

ated control pulses over a single channel, each Still a. further objectof the invention is to pulse being a complete signal. apply to a,sing1ewire a succession of electrical 5 An object of the invention is toconvey along a pulses of -varying electrical magnitude, to convey singlechannel a sequence of electrical pulses, the pulses t0 enOlfheIpOiIlt,and there apply the each signal pulse being a complete signaladaptsuccessive pulses in sequence t0 a pluralityof ed to producedifferentiated results at a remote responsive devices, the respectivedevices being receiving point. v Operable by vpulses of differentmagnitude, eaehrlo Still another object t of this invention is todisdevice being adapted to put out of operation .those tinguishdifferentsignal pulses in terms of the devices which are operable byvlower magnitude magnitudes thereof for the production of `differentDlllSeS-o I e effects at a, receiving point, Still another object of theinvention isito con- A furtherobject of this invention is to initiatevey over a cable single electrical pulses of nonat a transmitting ypointa plurality of signals of significant or uniform time duration and ofsigdiiierent electrical magnitude; to convey the significant electrieelmagnitude furthe conveyance nais along a single channel; and totranslate the of intelligible signals, which may be 'utilized forvvarying magnitudes 4into varying responses at a o the operation of aprinting telegraph.

receiving point.` Another object of the invention is to transmit 20Another object ofthe invention is to transmit over a single line aplurality of electrical pulses over a single wirel circuit a pluralityof electricall of nonsigniiicant time duration and signiilcant 1 pulsesin. sequence, successive pulses having dit- .electrical magnitude atlow, closely spaced elecferent electrical magnitudes; and to translatethe trical magnitudes, tor amplify the electrical magrespectivemagnitudes into predetermined renitudes to higher values and increasethe spac- 25 sponses at a receiving'point. ings there-between. andthereafter -to utilizethe Another object4 Yoi? the vinvention is tooperate e amplied electrical magnitudes for the operation Vany one of aplurality of devices selectively lby of predetermined magnituderesponsive devices,

means of the electrical magnitude of a signal, each different signalmagnitudecausing the opthe signal magnitude being sufficient to operateeration of a. single predetermined device. y l 30 a predetermined deviceand those devices oper` `Still another object oi the invention is toopableby a lesser signal magnitude being prevented rerate a typewriterat a remote point by means of from operating by the operationv of thepredea plurality of single electrical pulses of nonsigtermined device. lniilcant time duration and of signicant elec- 'A stiu further object ofthe invention is to tricai magnitude, each type key being nierateeiA 35respectively operable by predetermined signal transmit over a single:wire circuit a plurality of by a current pulsefof a predeterminedmagnitude electrical pulses of varying electrical magnitude,v diflerentfrom the magnitudes required for the and to utilize the successivepulses for the selec- Operatin of an if the other keys, tive operationof a plurality of responsive devices Stm luther abject of the inventionis to operate a printing telegraph device by `means yoi av plurality o!electrical pulses, the respective types ofthe printing telegraph beingselected by choice Another object of the invention is to set up a ofthe' magnitude or the electrical pulses trans' group of potentialvresponsive devices such that at taemgc invention isto tran a givenpotential applied to the whole group will i ano l t? l; I to u, tels'actuate only one thereof. m t digit se ec ng pu ses as or au ma c e" Afurther object of the invention is to conphone dwing by pulses ofpredetermined elec' nect a plurality of electrically responsive devicestric magnitude each die being represented by in parauei to a singlecircuit for the-application e Single Pulse 0f *i dem@ electric-a1magnitude 5 simultaneously to ou thereof of a plurality or Still anotherobject of the invention is te in electrical control pulses,` the devicesbeing so arlllete electl'lcl pulses 0f Varying magnitude Wc.' rangedthat some may not, be operated by a cordingtothe electricalindicaticn oiaphoto-ce)l, pulse, others may be operated by a pulse, thereby totransmit these pulses to a remote point, and to` producing a line ofdivision between those operoperate a predetermined one of a plurality o!magnitudes, and to render inoperable all the responding devices exceptthe one operable by the signal magnitude transmitted.

vdevices according to the magnitude of the electrical pulse initiated bythe photo-cell.

Still another object ofthe invention is to proto use the mechanical orelectrical movements directly or to control electricalor othermechanical functions.

In the prior art of signal conveyance, it has been found convenient toconvey control signals in a variety of Ways, successive independentpulses being used, such, as for instance, the telegraph code, in whichtime durations of succesive pulses and spacings are utilized for theconveyance of information, and such as the iive unit code, in

which the presence or absence of pulse at synchronized`intervalsdetermines the character of signals conveyed. Both of thesemethods involve a determination of-elapsed time in the course of signaltransmission which is often undesirable. Other control circuits requirea'large number of wires, a separate wire or circuit being provided foreach control function. -Still'other control systems utilize relay chainsof various forms in which the relays are actuated in successionaccording to the duration or sequence of the current pulses controllingthem.

'I'he device of this invention provides a simple control system in whichthe information! or control factor is conveyed in terms of electricalmagnitude, instead of in terms of time or sequence or relay chains as-inthe prior art.

Thus the device of this invention provides means by which a givenelectrical magnitude may be made to convey a given signal, or tocontrola given operation while a second slightly dliferent -electricalmagnitude carries a different item of information or effects a differentcontrol.

That is, broadly, the device of this invention makes it possibleto applyto a` given circuit a certain electrical magnitude, which may be a smallnumber of volts, which, when so applied; by the device of the invention,will actuate a given member; and a second slightly dlil'erent electricalmagnitude, a higher or a lower voltage, will actuate a different member;still another voltage will actuate another device and so onover a rangeof voltage steps, both the number and size of the steps being determinedby the insulation resistance of the system, the current carryingcapacity, the characteristics of the component parts, and the otherusual electrical factors.

The invention may also utilize, in combination with the voltageresponsive devices, anampllfying member adapted to increase themagnitude oi electrical values applicable to the device, thereby makingit possible to utilize a large number of closely spaced voltage steps atlow voltage for transmission, and to increase the magnitude byampliiication at the receiving device to `insure accuracy of operation.

- ably of direct current.

Fig. 3 is a circuit diagram of a device illustratv ing the inventionappliedto a radio signal channel. Y

Fig. 4 is a diagrammatic representation of an embodiment of theinvention as applied to the sending and reception of automatic.telephone dialing or pulsing signals.

Fig. 5 'is a diagrammatic representation of an embodiment of theinvention, utilizing a photocell for the control or' production of thesignal voltage.

The present invention utilizes electrical pulses of different magnitudesfor .the conveyance of the desired control or information signal. Asingle circuit may be used between the sending and receiving points,over which may be conveyed successive electrical pulses for thesuccessive sig-f operation being represented by a pulse of predetermineddifferent voltage. Such signals are conveniently obtained by the closingof keys connected to different points in a chain of series connectedbatteries, or from keys connected to successive points on apotentiometer resistance energized from any convenient power source,prefer- One end of the potentiometer maybe connected to ground or to areturn wire. The several keys are then connected in parallel to a linewire and serve to transmit ov'er -the line wire the desired pulses,controlled in voltage according to the desired signals or actuation tobe obtained.

At the remote end of the line wire there is provided a receiving systemhaving a plurality of devices respectively responsive to differentvoltages, sothat a low voltage will actuate one response device, ahigher voltage will actuate another, and a still higher voltage will'actuate still another, the vnumber of devices, and of differentvoltages, being determined by the number of signals to be transmitted,or of operations to be obtained.

In view of the fact that a device that is responsive to a given voltageis usually also responsive to higher voltage, the invention providesadditional means to prevent the operation of more the actuation of thosedevices, which are adapted to be actuated by lower voltages.

Simple control system Of the preferred embodiments of the inventionherein illustrated and described, the simplest form of the device isshown in Fig. 1. `Referring to this figure, a potentiometer resistanceR, is provided through which an electrical current is caused to flow bya source of current, which may be a battery B, or maybe any convenientpower source (a direct current generator, or a rectifier). A pluralityof taps are connected to the potentiometer vR and lead to the keys K.The other terminals of the keys K are connected to a common lead L,which, in turn, is connected to the line with the positive and negativepoles connected, as shown. 'I'he negative end of the potentiometer isgrounded at G, as shown, or may be connected to a return line and, forreasons which will later appear, it must be the negative end. It may benoted that the first of the keys K is not connected at the grounded endof the po'- tentiometer resistance R, but is connected at a point ashort distance away, so that the closure of the rst key Kl applies adenite voltage between line and ground. Similarly, the closure of key K2applies a still larger voltage between line and ground and, so on, eachkey thus applying its characteristic voltage to the line, which voltagemay conveniently have values in an arithmetical progression.

At the receiving end the device referred to utilizes a number ofgasdischarge devices, which number may be the same as the number of keys Kat the sending point. While any gas discharge device which has a controlelement and a Vcircuit responsive thereto and which has such anoperating characteristic that the controlled circuit passessubstantially no current until the control element has reached a certainpredetermined narrow range of electrical potential, and vvthereafterpasses substantially full cunent, may be employed, the gas dischargedevices illustrated are of the type known commercially as 'I'llyratron,and consist of an envelope containing a low pressure of vapor, such asmercury, argon,

etc., and a plurality of electrodes consisting of cathode, grid andanode. These devices are of the type which show practically noconductance when the grid is more negative than a s peclc .value andpass full current when the potential on the grid reaches or exceeds inthe positive direction the specific or critical value peculiar vto thedevice.

If, as illustrated, a hot cathode type of gas discharge deviceis used,'the cathodes of the entire group may be connected in parallel, as isindicated in Fig.' 1, and may be energized from any convenient powersource such as an alternating current line, (with a transformer toprovide the proper voltage).

t Another potentiometer RR is provided at the vreceiving point, whichmay also be energized by any convenient power source such as aV batteryBB. It may be noted that the poling of this bat-f tery, in common withthe battery B at the send.`

ing point is of consequence, the positive end of the battery BB beingconnected to the grounded end of the potentiometer RR. The successivegas discharge devices Tl to T5, inclusive, asshown, are equipped withconnections from the respective grids thereof to successive points onthe potentiometer RR. It will be noted that the \sucfcessive points ofconnection of the grids of the tubes of the gas discharge devices TI toT5, inelusive, are connected successively at more nega` tive points and,accordingly, the respective grids are biased negatively by higher andhigher values. Each device T has in its plate circuit a relay memberindicated by the reference characters Mi to M5, inclusive.

Each ofthe relays M has two pairs of contacts, one pair being normallyclosed when. the relay is unenergized, and the other pair being normallyopen when the relay is unenergized. In addition, the construction of therelays is such that upon energization of the relay, the rst mentionedpair of contacts is opened at once, while the second mentioned pair ofcontacts is closed only after a brief time delay.

The relays M may be of a solenoid type, as indialso be obvious. of therelay may be increased either by the type cated diagrammatically in Fig.1, in which the prompt opening of one pair of contacts, and clos- .ingof another pair of contacts after a brief time of winding, themechanical construction, or by the use of damping rings to obtain thedesired delayed action in the latter part of the contact operatingstroke. Alternatively, a pair of relays may be utilized, one adapted toopen a pair"of contacts upon energizationQwith a minimum of timedelay,.the other adapted to close a pair of contacts after a small timedelay. In such a system the second relay may be operated from circuitclosing contacts on the first relay.

The several plate circuits of the gas discharge devices T are connectedthrough the windings of the several associated relays to the currentsupply. The normally closed contacts of each relay carry the current forall of the relays in circuit with gas discharge devices having lowernegative biases on the grids in such a way as to open. the platecircuits of all the less negatively biased devices when any one operates(except, of course,

the lowest biased device, which has no 'associated' device with a stilllower bias). This action is apparent from the diagram of connectionsshown in Fig. l.

Y The source of anode power for the system illustrated preferablyprovides alternating current because of the fact that this gives acessation of current flow during each cycle (the gas discharge devicebeing unilaterally conductive, current does not flow during the reversehalf of the cycle). This is advantageous because of the fact that, i!direct current were used with the commercially known Thyratron gasdischarge device illustrated, means would be required to interrupt the current flow in the tube, since this gas discharge device does not ceaseto carry current when the bias upon the grid is returned to its negativevalue. Obviously if mechanical marginal relays are employed, or gasdischarge devices in which the plate current is interrupted when thegrid is returned to a negative value, direct current mayl be used in thecontrolled or anode circuit without the use-of supplemental means forinterrupting the flow of current therein. It may be noted that thecircuit illustrated is substantially a self-rectifying circuit and eachgas discharge device provides its associated relay with rectifiedcurrent. Because of the requirement that the relay have a fairly steadycurrent in order to complete the delayed latter part of the stroke, thecondensers CI to C5 may be included in the circuit to form with therelay winding a simple smoothing lter.-

v G, the several rsistances for the several tubes being indicated at Gito G5, inclusive. These grid resistors are inserted to limit the gridcurrent, which might otherwise tend to flow when the device becomesconducting. Under such circumstances, the presence of a substantial gridcurrent would cause excess current in the potentiorneter RR, andunbalance the bias voltages.

'Ihe upper contacts of the respective vrelays MI to M5, inclusive, maybe utilized for the closing of any desired circuits; alternatively. themovecharge devices T assume the potential set by the points to whichthey are connected on the potentiometer RR, the relative gridvoltagesbeing determined by the relative connection points, and theactual voltages being determined in'addition by the voltage of thebattery BB. In normal nonoperated conditionLall of the biases applied tothe grids of the several gas discharge devices are more negative thanthe critical point, and, accordingly, none of the devices pass current;all of the relays M are unenergized, and all of their lower contacts areclosed, permitting the application of voltage from the anode powersupply source to the respective anodes of the devices.

The closure of a key K applies a positive voltage tothe lead L and tothe line, which voltage, in turn, is conveyed by the line to thepotentiometer RR.

It will be noted that the common cathode lead of all of the gasdischarge devices T is grounded,` thereby setting the potential of thecathode. The positive end of the potentiometer RR is grounded through aline resistor LR. Accordingly, in the absence of a voltage applied totlie common lead L by vclosure of a key K, the positive end of thepotentiometer RR is likewise at ground potential, and all of the gridsof the tubes T are at potentials more negative than ground, morenegative than the cathodes, and more negative than the line.

I Application oi a given positive voltage to the line by closure of oneof the keys K raises the potential of the positive end of thepotentiometer RR by an amount depending upon the relative resistance ofthe line and the resistor LR, and

bearing the same ratioto the applied voltage, that the resistance of LRbears to the combined resistance of the line plus LR. A fixed percentageof the voltage applied to the line thus appears as a voltage drop acrossthe resistor LR and is available to change the over-all potential of thegrids of the tubes T with respect to their cathodes.

In the commercial form of gas discharge device, sold under the tradename, Thyratron current ow begins when the grid has approximately thepotential of the cathode. In the embodiment shown in Fig. l, thepotentiometer drop between the positive end of the potentiometer RR andthe point of connection to the grid of the least negatively biased tubeis less than the voltage drop, which will be produced across theresistance LR by the lowest voltage applied to the line by closure ofone of the keys K. Thus, when key Kl. is closed, a definite voltage, asdetermined by the potentiometer R, is applied to the line. The voltagedrop appearing across thte resistorLR then serves to make more positiveall of the voltages delivered to the respective grids by thepotentiometer RR. This value, upon closure of the key KI, is adjusted tobe sumcient to make the grid of the tube TI positive by a suillcientamount to permit current ow therethrough. 'I'his current flow energizesthe relay MI, and closes its contacts to actuate any desired device.

Closure of the key K2 impresses upon the line an appropriately higherpositive voltage. which voltage produces an increased drop across there'- sistor LR, the increase being equal to the difference in bias onthe grids of the devices Tl and T2. Accordingly, not only is a positivebias applied to the grid of the tube Tl, but a positive bias is likewiseapplied to the tube T2, and both become conducting. Both, therefore,energize'thelr respective relays MI and M2. However, the initial rapidactuation of the relay M2 opens its lower contacts,`thereby interruptingthe power supply to the tube TI and deenergizing the relay MI before ithas completed its full stroke. The relay M2, however, `completes itsfull stroke, closing its upper contacts to perform the functions desiredto be produced by the closure of the key K2.

Closure of `the key K3 gives a correspondingly still higher voltage dropover the resistor LR, which is adjusted to be sufficiently high to bringthe grid of the gas discharge device T3 to the positive condition.Current will then start to ilow .through the devices TI to T3. Relay M3is energized as before indicated for relays MI andyMZ and opens thesupply circuit to both devices TI and T2. As previously described thispermits the complete operation of relay M3 to close its upper .contactswhile deenergizing the relays MI and of gas `discharge devices islimited only by such factors as the permissible circuit voltages acrossthe keys K, thepermissible biases upon the grids of the devices T, andthe minimum voltage steps between successive grid biases, and anydesired or appropriate number up to the limit set may be utilized. Itwill be understood that the gas discharge device begins its currentconduction at a fairly sharp critical voltage point, but this criticalvoltage has a small range. The dicrence in the bias of the successivegrids must be substantially greater than this smally voltage range. Thisfactor, which is a structural characteristic of the tube is acontrolling factor in the closeness of spacing of the taps on thepotentiometer RR. In combination with the permissible voltage upon themost strongly negatively biased grid, and themaximum allowable voltageon the devices, which can bey utilized, it determines the maximumynumber` of signals which can be transmitted, or the maximum number ofoperations which can be controlled.

While in the preferred form of the invention just described a particularrelay device has been referred to, it is obvious that the invention isoperable with any relay device which has a control circuit and a circuitresponsive thereto, and which has such an operating characteristic that.the controlled circuit passes substantially nocury system.

passes substantially a full predetermined current. In the preferredembodiments of the invention illustrated and described herein thecommercially available gas discharge device sold under the trade nameThyratron has been used as an example, because it has the aboveoperating characteristic. Discharge devices or electronic tubes havingthis characteristic are referred to herein as of the trigger actiontype. It will also be apparent that for the purposes of thisinventionthe only trigger action essential is one which permits full current toilow suddenly in the controlled circuit when the controlling elementreaches the critical potential, irrespective of whether the reverseaction takes place or not. If the reverse trigger action does nottakeplace, as is the case with the '-I'hyratron, then as already described,the controlled circuit may be interrupted by using alternating orperiodically interrupted direct current, in which event it interruptsitself when the potential of the control member recedes below thecritical value. If a gas discharge device is used in which the reversetrigger action takes place, then obviously to interrupt the controlledcircuit it is only necessary to return the control element to thecritical value for shutting off the current in the controlled circuit,and uninterrupted direct current may be used in the controlled circuit.In summary, the system of the invention thus provides a pluralityv ofgas discharge devices which, in non-operating positions, carry nocurrent, and which have the grids thereof. respectively diiferentlybiased, so that the application of positive potential to the system willcause some or all of the grids to assume a potential which will permitcurrent flow through the corresponding devices. Each of the devices hasyan associated relay adapted to operate contacts to open the anodecircuits of -all of the devices which have less negatively biased grids.Accordingly, upon the application of a voltage pulse to the system oneLor more of the devices may start to carry current. However, the quickacting relay opens the anode circuit of all but one of the devices whichtend to operate, and, accordingly, but a single one of the associatedrelays is energized. By this arrangement, it thus becomes possible tocause a single relay to close upon the application of a pulse ofpredetermined voltage, and to provide thereby for the selectiveoperation of as many other relays as may bedesired. Thus, a given relaymay be selected by the choice of the magnitude of the voltage pulseapplied to the 'Amplifier combination The device of the invention may becombined with other devices for the production of other specializedresults. 'In some instances, the permissible maximum voltage, which maybe applied to a given line, is limited by the characteristics of theline, and the number of steps of voltage to provide for l,the desirednumber of different signals may be such that the difference in voltagebetween successive steps 'is less than that required by the system todistinguish accurately between the several signals to be sent. Thisinvention, therefore, further includes the combination of the pluralityof voltage pulse responsive devices, as above described, with anamplifier system adapted to increase proportionally the magnitude of theseveral voltage pulse signals. This arrangement is particularly shown inFig. 2, in which there is disclosed a system similar to that of Fig. 1,including'the plurality of keys, gas discharge devices, the associatedrelays, potentiometers, and grid resistors with connections in generalsimilar to those previously shown. Interposed between the line and theresistor I4 which replaces the line resistor LR of Fig. 1 there is,however, positioned an amplifying system A.

'I'he amplifier A may consist of a single amplier tube II, or mayconsist of a plurality of such tubes, according to the requirements ofthe system. The line .over which the signal current is to be transmittedis connected-to the grid of the tube I I, in parallel with the resistorI2, which corresponds to some extent, to the line resistor LR of Fig. 1,in-that it causes the application of voltage to the grid of the tube IIwhen a key K at the sending point is closed. The' resistor I4 isconnected in the anode circuit of the tube, and a bias battery C isconnected in circuit with the amplifier tube grid.

' The system above described is essentially a resistance coupledamplifier system in which the resistors I2 and I4 correspond in generalto the line resistor LR of Fig. 1, but the interposed vacuum tube causesan increase in the electrical magnitude of the voltage applied acrossthe resistor Il. A direct coupled amplifier is desirable in systems inwhich random or low frequency pulses are to be amplified and isconvenient for any frequency. However, in systems in which a rapidsequence of pulses is to be transmitted, as may occur with highspeedtelegraphy, satisfactory results may be obtained by the use ofv anamplier in which the coupling between successive stages, the input line,and the voltage responsive devices, is obtained by inductive ortransformer coupling, or by capacitive or condenser coupling. Theselatter forms of coupling, however, are useful only in the event that thesignal pulse occurs at a relatively rapid rate, since such amplifiers donot normally function for the amplification of sustained steady values.

In this embodiment, the positive pulses delivered by the keys K, producea voltage drop across the resistance I2. 'I'he bias battery C isdesirably of such a voltage as to nearly block the tube II, allowingsubstantially no current to iiow therein, and in the resistance I4, inthe absence of signals. Upon the arrival of the positive pulses from thekeys K, the grid of the tube II is made less negative, allowing currentto ow in the tubes II and the resistance l5, thereby delivering ampliiedpositive pulses to the potentiometer RR.

and the gas discharge device. These amplified voltage pulses thenproduce therein similar reaction to those described in connection withFig. 1.

'I'he system above disclosed is particularly advantageous in connectionwith cable signaling devices, as is also shown in Fig. 2. In thisembodiment, a similar form of sending system may be utilized tothat-shown in Fig. 1 consisting of a plurality of keys K, and a similarpotentiometer R, energized by a suitable source of curreni, as a.battery B. The variable voltage pulses are applied to the cable asshown, and conveyed therethrough to the amplier A, by which they areincreased proportionately in electrical magnitude to a desired value andapplied to the resistor Il, corresponding to the line resistor LR ofFig. 1. The voltage drop in the resistor I4 from the plate current inthe tube I I changes the effective potential upon the potentiometer, RR,and one or more of the tubes T tend to vresistance coupled amplifier isdesirable.

figure there is outlined a radio transmitting'systern adapted totransmit radio signals modulated in amplitude according to the relativevoltage delivered thereto from the keys K, and a receiving setresponsive to signals received from the sending set, adapted to deliverelectrical pulses of differing magnitudes according to the amplitude ofthe received radio signals.

A plurality of keys K are provided as in the embodiment of Fig. l, andare associated with a potentiometer, R, which is energized by a powersupply B, as before described. Closure of any one of the keys K deliversa voltage pulse of corresponding magnitude to the radio transmittingapparatus.

The transmitting apparatus, oscillating system,

high frequency oscillations by an amplifier of the type shown in Fig. 2,if the signal strength to be transmitted makes amplification desirable.Obviously the coupling between successive amplifying stages and betweenthe amplifier and modulator circuit must be adapted to the type of pulseto be amplified. If these pulses are of low or random frequency, adirect coupled gi they occur at relatively rapid rates a capacitive orinductive type of coupling, as previously suggested, may be utilized.Also, the signal may be amplified at radio frequency after modulation.In any event, the system required is one which will convert voltagepulses of different magnitudes into radio frequency oscillations ofcorresponding'amplitude. I

The receiving member maybe of any convenient type of radio frequencyreceiver, which may include amplifier members for amplification at radiofrequency, and an output detector or rectifier. The output deviceis'desirably associated with an output resistance corresponding to theline resistance LR of Fig. l, byf which a varying amplitude of highfrequency signal applied to the detector device produces a proportionateunidirectional voltage pulse in the form of a voltage drop acrosstheoutput resistance. This voltage drop across the output resistance may beamplified, as shown in Fig. 2, or may be utilized directly for theoperation of the selector device corresponding to that shown in Fig. l.

`By this embodiment of the invention, the desired signal originating asa voltage pulse may be converted. to a high ,frequency oscillation ofcorresponding amplitude, transmitted over a radio channel, received at aremote point, detected or rectified, reconverted to a correspondingvoltage pulse and applied as a voltage pulse to the voltage responsivemember of the invention to cause the selective operation of apredetermined gas discharge device and the predetermined operation of asingle relay assembly for the production of a' predetermined signal, ora predetermined operation as previously described.

Telephone pulsing The system of this invention is convenientlyapplicable to the transmission of automatic telephone control signals.For this purpose a device may be provided at a subscribers station, or

at a telephone exchange, adapted to send single electrical pulses of amagnitude varying accord- 'I'he voltage pulse may be amplified before itis caused to modulate the may be vreceived at a central exchange orbranch exchange and utilized to control the selection of the calledsubscriber. For this purpose a de'- vice similar to the receivingportion of Fig. 1 or Fig.'2 may be utilized with such changes as arenecessary for the purpose, which will be indicated in the followingdescription. This device may take any one of many forms, which will beobvious to those skilled in the art, its basic usefulness depending onthe fact that it will close any selected one of ten or more line, ortrunk selecting, circuits.

Referring to Fig. 4, the subscribers instrument may consist of the usualcall bells 2l, condenser 22, induction coil 23, receiver 24, transmitter25, and hook switch 23. These may be connected in any one of the usualways, as, for instance, in the manner shown, which is very commonlyused. In addition to the usual equipment there is also provided aplurality of push buttons 3l, 32, 33,

etc. Inthe drawings, for the sake of simplicity only five of these areshown to illustrate theprinciple. In practice any convenient number maybe employed, as, for instance, ten, for opera- -tion in the decimalsystem of numbering. There is also provided an extra pair of contacts 21and 28, on the hook switch adapted to close a circuit when the receiver'is raised.

Associated with. the push button is a resistance SR, tapped at as manypoints as there are push buttons, 2|, 22, 23, etc., the pointspreferably having equal resistances between them. This resistance shouldpreferably be quite high in comparison to the line resistance. One endof this resistance is permanently grounded, as shown.

With none of the push buttons depressed, one Wire B of the subscriber'sline goes directly to the receiver, transmitter, etc., while "the Votherwire G goes through contacts on each button connected in series, and,finally, also to the receiver, transmitter, etc.

It is to be noted that the wire B that goes directly to instrument istheone which is connected to the positive side of the common battery CBat the telephone exchange, and the system rcquires that the negativeside of this battery be grounded. The other wire G is ultimatelyconnected to ground at the exchange. l

When the receiver is lifted from the hook, the hook switch, through thesprings 21 and 2B, completes a circuit from the battery side of thevline to the push buttons, as shown. This makes the push buttonsinoperable unless the receiver is off the hook. When one of the buttons2|, 22, 23,

etc., is depressed, the right hand springs connect the ungroundedf'endof the resistance SR to the battery side of the line, through springs 2land 28. In this position the exchange battery, the battery side of thesubscribers line, and the resistance SR, cooperate to form a simplepotentiometer circuit, the resistance being bridged across the batteryby having one of its terminals connected to the positive side of thebattery through the line wire E, while its other terminal is connectedVto the negative side of the exchange battery through their commonconnection to ground. The left hand springs of the depressed buttondisconnect the line wire G from the instrument and connect it to oneofthe taps of the ing to the digit to be indicated. These pulses is to benoted that the left hand springs of the push buttons are of thefhnalrebefore break" type, so that the operation of any push button does notbreak the linecircuit once it is established by removing the receiverfrom the hook. The necessity ior this will appear later.

The net result 'ci' the scheine ci? connections shown and described isthat provides a conventional type of subscribers circuit when no buttonis pressed. `when the receiver is iiited oit the hoch and a button ispressed., the tele phone instrument proper is disconnected from theline, while the resistance associated with the push buttons is convertedto a potentiometer', fed from the central cnice battery over one or" theline wires with ground return. The other line wire serves as thevariable potential lead from the potentiometer and carries bach to thecentral oihce a potential depending upon the button pressed, within thelimits ci the central otu tice battery. This part of the apparatus is,therefore, a counterpart of sending lteys, asz scciated potentlorneters,etc., shown in Figs. l., 2 and d, in other embodiments of the invention.

it the central cnice or sub-station, the two line wires pass through achain ci contacts of the selector relays C) in the manner shown. Theside of the line which feeds the potentiometer in the subscribersinstrument then goes to the positive side of a source ci direct current,which may conveniently be the central office coinmon battery, thenegative side of this battery (or other source) being grounded. Theother line wire terminates at a resistance LR, the other terminal ci"which is grounded. This resistor is similar in iunction to theresistance LR of Figs. l and 2.

Connected to the saine terminal LR with the line wire is a potentiometerRR, which is the saine in function and purpose as the similarly letteredpotentiometers of Figs. l and 2. it puts successively larger negativebiases on the grids of the tubes Till, T32, T35, Tdt and Titti.

,it is to be noted that the number of tubes is one greater than thenumber of push buttons, and that the tube having the highest negativebias has alternating current supplied to its anode. y.all the rest oithe tubes are supplied with direct current anode power, which, forconvenience, is shown as coming from the common battery CB citheexchange. This anode supply oi direct 'current passes through maltecontacts oi a relay Siti, placed in the G side of the subscribers line,the purpose of which will presently appear.

e relay til is shunted by a condenser to reduce the line impedance tovoice currents.

The manner ci operation of the apparatus is as follows: when thereceiver is lifted from the hook, a circuit is formed from the positiveside of the battery CB, through the B side of the subscrlbers line.through the subscribers instrument, through the G side of the line,through LR and back to ground. This completes the circuit, since thenegative side of CB is grounded. The resistance of LR. is so high thatit constitutes by far the greatest part of the resistance of this entirecircuit, hence, almost the full voltage of the battery CB appears as a.drop across LR. This ls sumclent to overcome the bias of the entirechain of tubes T, including T36, which has the highest bias in thechain. This permits current to flow through all the tubes and theirassociated relays N. which are quick acting and correspond to the quickacting 'relays N of Fig. 2. However. one set of contacts of the relayN36 interrupts the anode current for all the lower biased tubes in. thechain, as already described, and prevents the operation of all therelays N (except, of course, N35). The other set of contacts of N36passes current through the slow acting relayv Ote, which corresponds tothe relays O of 2. This relay now pulls up, connecting to the line thetone circuit. This tone circuit sends out over the line the well knowndialing tone, indicating that the line is ready for use. in the eventthat this apparatus should be used in connection with an automatic linender or selector switch of the type now in use, this feature would beparticularly desirable, as it would cause the subscriber to wait untilthe line nder had operated, before operating a push button.

When the subscriber hears the ready tone, hepushes a buttoncorresponding to the rst digit of the number he desires, for example,the button St. This disconnects the instrument from. the line and putson the wire G a corresponding potential which is lower than that eX-isting when the instrument was across the line. This lower potential isinsufi'icient to overcome the bias of tube Tilt. This tube, beingsupplied with alternating current therefore ceases to con duct. curr-entat the next half cycle when the anode becomes negative. This causes thearmature or relay Ns@ to drop back, the relay reconnecting the directcurrent to the anodes of the preceding tubes T. Y By the method alreadydescribed, the relay corresponding to the button it now pulls up andpermits the complete operation of its asso ciated slow acting relay034i. The closing of relay @Sli connects the subscribers line to thecorresponding selected line L36, Vwhich may be directly the line of thecalled subscriber, or which may merely lead to a group of lines ortrunks from which further selection may be made by again pressing one ofthe buttons Si, 32, etc., accordingly, to the next digit of the numberto be selected.

Since the tubes T (except T36) are supplied with direct current at `theanodes, the re-establishment of the negative bias on their grids doesnot interrupt the anode current; hence, the selected relay (Nitti inthis case) remains energized after the corresponding button is restoredto its normal position.

The operation of any of the relays O also connects to the-subscribersline the repeating coil, di, which, through its connection to thebattery CB, furnishes the proper current to the line for energizing thecalled and calling subscribers instruments. This repeating coil need beconnected to the contacts of the relays O, however, only if these relaysare used to'select subscribers lines, that is, if they respond to thenal digit of the called number. If the relays O are used forintermediate digits, the coil 4| and the corresponding contacts of therelays O may be omitted. By this arrangement only one repeating coilwill supply current to the line, and that coil will be connected at theselector relay of the last digit in the number. l

It will be noted that the anode current for the tubes T comes through acontact of the relay 30, which is connected in series in the'subscribers line, and so arranged that the tubes T are supplied withanode current only when the relay 30 is energized. It has also alreadybeen pointed out that the buttons 3|, 32, etc., have make-beforebreakcontacts, hence, the pressing of any 'of these buttons does not evenmomentarily open the 2,oos,scs

linelr circuit, but merely changes the potential of the line wire G withrespect to ground. The relay III, therefore, continues energizedthroughout lall the operation of the buttons, as long as the receiver isoil? the hook. When the conversation is completed and the receiver isrestored to the hook, the relay 3U is de-energized, the supply of anodecurrent to the tubes T (except T36) isv rent, to operate in series withthe resistance LR.

Relays operable on very small currents are, however, commerciallyavailable, or the relay may conveniently be replaced by a suitablepotential operated device, such as a vacuum discharge or gas dischargetube. As already explained, the line G is vat ground potential only whenthe receiver -is on the hook, and thereafter is continually at somepotential higher than ground. The-grid of a triode may, therefore, beconnected to the line wire G in place ofthe relay 30, and the change ofpotential thereon utilized to operate a relay in the anode circuit, thisrelay th'en performingl the function indicated as performed by relay l0.

It will also be apparent that in the above described embodiment, if eachof the lines L3 I L32,

L33, etc., lead to another selector circuit, then, 4 if one ot thebuttons 3|, 32 etc., is held down too.

long, it may also operate a selecting relay O in the next selectorcircuit, thereby causing an error.

".l'o obviate this, each successive selector circuit after the nrst maybe provided with a device,

which will keep it disconnected from its corre-y -spoiiiding resistanceLR., such as contacts on an appropriate relay, until Yafter the linewire G -ha's attained its highest potential, which occurs when none ofthe buttons are depressed and only the instrument is across the line.With -this arrangement the pressing oi a button once will then operateonly one selector relay no matter how long the'button may be keptdepressed. To operate the next selector-relay in the chain,corresponding to the next digit in the number, it will be necessary tolet .each button come back to normal before pressing it, or anotherbutton, again. This action restoressthe khighest available" potential toline wire G, and permits the resistorA LR of the circuit last selectedto be connected ,to that circuit. Means for,causing each successiveselector circuit to remain disconnected from its resistance LR untilVafter the line wire Gf has attained a certain fixed potential, arereadily available and will suggest themselves to those skilled in theart, and need not be here described.

The purpose of the foregoing description, relating to telephonesignaling, has not been toshow a ilnished system of'automatic telephony,coml Y 1t viriiiaiso pe obvious to those skiiied in the art thatalternate methods may be used other than those suggested, withoutdeparting from the spirit Vof the invention. As an example, thepotentiometer at the subscribers instrument may be powered by a localbattery, the vsystem may be used in a'local battery or magneto exchange,or it may be used with particular advantage over long distance lines,with or without a common battery at the exchange.

Thus, the system of the invention maybe used y to enable a subscriber,by suitable operations at his instrument, to select any one of aconsiderable number of lines leading to other exchanges orsub-exchanges, groups of lines, individual -lines, or selected means ofringing individual lines, and

to repeat this selection successively to `'effect the nal selection of asingle line, and mea'nsof ringing any party on .that line, out of anentire telephone system.

` l Light responsive system The basic elements of ihe'inventiondescribed with Fig. 1 maybe utilized in combination with a photo-cellsystem for other useful functions.

- A photo-cell` is responsive to light, permitting a ilow of electricalcurrent therethrough, which is vproportional to the illumination, a highillumination producing a larger current ow than a lesser illumination.When it is'desired to obtain responses in steps, depending upon thedegree of illumination, thel embodiment of Fig. 5 may be utilized. Asindicated, the photo-cell, which may be of the emission type,photo-galvanictype, or photo-resistor type,I is connected, as`shown,.toan ampliiier. As already explained in other embodiments of thisinvention, it is desirable that this ampliiier be'ofthe direct coupledtype in order that it may faithfully amplify sustained current orvoltage pulses, or pulses of random duration. Where the application issuch that the pulses will be suiiiciently frequent and regular, theninductively and capacitively coupled ampliiiers may be used. Theoutputor this amplier is connected to the resistor LR, corresponding-to thelineresistor LR of Fig. y1. The gas discharge devicesof 'Fig.1 areprovided, as indicated, by a box marked selector" shown in Fig.

5, and operated in a similar manner to close a circuit through therespective pairs of leads from the selector as indicated.

By this embodiment ofthe invention, agiven degree of illumination on thephoto-cell causes a corresponding currentiiow therethrough, which isamplined and caused to `yield a suitable/poltage drop over theresistance LR, which, in turn, .causes the actuation of one of the gasdischarge devices T, as shown in Fig. 1, and the actuation of thecorresponding relay to close a circuit to the desired operabledeviee. Ahigher degree of illuminationV produces a higher current ilow throughthe resistor LR and closure of the lcorreshades, orlight reflecting, ortransmitting power,

or color.4 Light from the sortable objects may be caused to impinge onthe photo-cell, to cause the corresponding current ilow therein. Thiscurrent flow produces a voltage drop-in theresistor LR, which causes theappropriate relay T to operate and close its contacts. Closure ofcontacts may thenbe used to produceany desired operation, such as theselection of sorting pockets.

This sorting operation may be conducted accord` ing to the reflectingpower of the object, or according to its optical density, its lighttransmissive power or according to the presence,- or absence, or size ofopenings therein.

Alternatively, the device 'may be utilized ior the control of variousmembers according to the intensity of illumination, such as the turningon and oi of successive steps of artiilcial illuminationpas the naturallight in a given place varies, or such as the control of window shades,etc. It may be notedthat this device is one of the few available deviceswhich are adapted to respond to vdeilnite discrete steps over the rangeof a continuous change of illumination, and that it responds insuccessive steps to the exciting energy changes..

- Remote control Manyother uses of the system of this invention will b eobvious, among which may be mentioned the use ofthe system in duplicatefor remote control operation over a single line, of electrical switchesat a sub-station or unattended generating station from a inain loaddispatch center with automatic answer back, upon the occurrence ofchanges at the remote point, the controlof selected mechanicaloperations from a distance, such as the opening oi. selected chutes oroutlets, etc., or the opening of valves in piping systems, the throwingof switches of various sorts and many other uses, which willoccur-tothose skilled in the art.

The device of this invention thus- :provides simple means for thetransmission of signals by single electrical pulses of differingelectrical magnitude, primarily differing in voltage, but signincantlydiffering in current, since diiferingcurrents are readily convertedAinto different voltages by the differing drops they produce alongv theresistances. The responses to these different voltages may be utilizedindependently for the control of a plurality of different predeterminedpulses in which the significant 4factor is electrical magnitude ratherthan the -time duration, as is necessary for most signal impulses oftheprior art.

Also since the general term gas discharge device has been used`heretofore to designate some electronic devices which do not possessthe operating characteristics previously referred to, the term gasdischarge device of the trigger action type", wherever it occurs in theclaims appended hereto, shall be taken to mean. an electronic or gasdischarge device having atcontrolled circuit responsive to a controllingelement and having the operating characteristic that the controlledcircuit passes substantially no current until the control elementreaches a certain narrow predetermined range of electrical potentialsand passes substantiallyl a predetermined current when the controlelement reaches-or'exceeds this range of potentials, further increasesin the potential of the control element being substantially means forsending a plurality of signicant pulses of din'erent electricalmagnitudes, and means selectively responsive thereto according to theelectrical magnitude for the production of predetermined responses, saidlast mentioned means comprising gas discharge devices of the triggeraction type.

2. An electricalsignaling system, comprising, in combination, means 'forsending electrical pulses of non-signicant timeduration and 'significantelectrical magnitude, and means selectively responsive to the electricalmagnitude of the signal, said last mentioned means comprising gasdischarge devices of the trigger action type.

3. An electrical system comprising means for the production ofelectrical pulses of diiferent electrical magnitudes, means for theconveyance thereof toa remote point, and means selectively responsive tothe electrical magnitude for the production of a predetermined response,said last mentioned means comprising gas discharge devices of thetrigger action type.

4. In combination, a plurality of circuit mem- ,bers respectivelyadapted to apply diierent electrinected in parallel to said circuitrespectively responsive to different applied voltages thereon, andmeans' actuated thereby for the production of a predetermined responseand for preventing a response by devices actuable by lower voltages thanthe predetermined voltages.

5. lThe combination of a plurality oi' gas discharge devices of thetrigger action type, means i'or normally `applying diierent biases tothe grids thereof, means responsive to current ilow in `said devices,and means for varying the potential of the bias producing means forovercoming the grid biases of said devices.

6. In combination, a plurality of gas discharge devices of the triggeraction type having grids, and anodes, means for applying diil'erentnormal grid biases to the respective grids thereof, means for overcomingthe gridf bias of said devices, and

, discharge devices of the trigger action type conmeans for causing onlyone thereof to pass curof a given indicating grid bias of a plurality ofsaid devices, and means for preventing the response of the deviceshaving lower grid biases.

8. Incombination, means for initiating a plu.- rality of electricalpulses of diil'ering magnitude, means for conveying such pulses to aremote point, a plurality oi' gas discharge devices of the triggeraction type at the remote point respectively independently responsive toa predetermined signal pulse magnitude, and members actuated by theresponse of saidgas discharge devices.

9. In combination, a signal sending mechanism comprising a potentiometerand a plurality of associated keys, a signal conveying channel and asignal responsive member comprising a plurality of normally differentlybiased gas discharge devices of the ltrigger action type respectivelyresponsive to different signal voltage magnitudes, means for preventingthe operation of more than a single one of the group of gas dischargedevices, and means for causing an operation in response to theoperations of the selected gas discharge devices.

l0. In combination, means for initiating pulses of varying electricalmagnitude, means for converting said pulses into oscillations ofcorrespondingr amplitude, means for receiving said oscillations, meansfor detecting said oscilla- 'tions and producing voltages correspondingto varying the potential of said bias producing means with respect tothe cathode of said gas discharge devices, said last mentioned meanscomprising a controllable voltage source.

12. In combination, a group of gas discharge devices of the triggeraction type having grids, means for producing a plurality of normallydifferent biasing voltages connected to said grids, relays associatedwith said gas discharge devices operable by -current flow therethrough,means for varying the potential of said bias producing members withrespect to the cathodes of said gas discharge devices, said lastmentioned means comprising a controllable voltage source, means forpreventing the operation of more than one of the gas discharge'devices,and means operable by said discharge devices for producing a givenresponse. y f

13. In combination, a plurality of gas discharge ,devices of the triggeraction type, a member adapted to supply differing grid voltages to theseveral devices whereby the several devices are differently biasednegatively, and means for supplying varying amounts of positivepotentials to the biasing devices to convert the biases upon' some ofthe grids from negative to positive values.

14. In combination, a plurality of gas discharge devices of the triggeraction type, a member adapted to supply differing gridvoltages to theseveral devices whereby the several devices lare normally differentlybiased negatively, means for supplying varying amounts of positivepotentials to the biasing devices to convert the biases uponA some ofthegrids from negative to positive values whereby current is allowed toflow therein, relay means responsive to current flow in said tubes, andmeans-operable by said relay for producing suitable responses andpreventing the flow of current through more than one gas dischargedevice.

15. In combination, means for producing signal pulses of varyingmagnitude, means for` amplifying the magnitude thereof, and meansresponsive in steps .to the amplied magnitude to produce' aresponseaccording to the magnitude of the original voltage pulses, said lastmentioned means comprising gas discharge devices of the trigger actiontype. f

16. In combination, a photo-cell member responsive to changes inillumination, and a device ycomprising a-plurality of gas dischargedevices of the trigger action type and respectively associated relaysresponsive individually in successive steps to the changes inillumination upon said photo-cell, said relays being adapted to beoperated thereby for the production of other responses.

1'7. I n combination, means for initiating electrical pulsescorresponding to intelligible characters, each character beingrepresented by a single pulse of a differenty electrical magnitude fromthose representing other characters, means for conveying said pulses toa remote point, a system comprising a plurality of members respectivelyresponsive to pulses of differing magnitudes, combined with means forpreventing the operation of more than one device in response to a givenpulse, and means actuated thereby for the recording of the variouscharacters indicated by the pulses.

18. In combination, means for initiating electrical pulses correspondingto intelligible characters, each character `being represented by alsingle pulse of a different electrical magnitude from those representingother characters, means for conveying said pulses to a remote point,comprising a cable system and means for controlling the pulse form, asystem comprising a plurality of members respectively responsive topulses of differing magnitudes, combined with means for preventing theoperation of more than one device in response to a given pulse, andmeans actuated thereby for the recording of the various charactersindicated by the pulses.

19. In combination, means for initiating electrical pulses indicating bythe electrical magnitude thereof the several numerical digits, meansresponsive thereto for determining the digit indicated comprising aplurality of gas discharge devices of the trigger action type andassociated relays, and means actuated for selecting and connecting apredetermined numbered circuit.

20. An electrical signaling system, comprising, in combination, meansfor sending electrical pulses of non-significant time duration andsignificant electrical magnitudes, and means selectively responsivethereto, said last mentioned means including gas discharge devices ofthe trigger action type responsive to all the pulse values above acritical value differentfor each device and mechanism associated witheach device for the production of a usable response and the preventionof response by a member having a lower critical value.

21. In combination, a plurality of gas discharge each of said devices,means for normallyapplyv ing diiferent grid biases to therespective'grids of said devices, means for overcoming the grid` bias ofa group of said devices, and means for preventing the actuation of theiirst mentioned means of all the devices of said group except the -onemost negatively biased.

22. In combination, a plurality of gas discharge devices ofy the triggeraction type having grids,

means responsive to current now `in said devices,

means for normally applying different grid biases to the respectivegrids of said devices, means for overcoming the normal grid biases of aplurality of said devices, and means controlled by the passage ofcurrent through one of saiddevices for preventing the passage of currentthrough the others.

23. In combination, a plurality of gas discharge devices of the triggeraction typehaving grids, individual means controlled by current now ineach of said devices, means foinl normally applying different negativegrid biases to the respective grids of said devices, means forovercoming the negative grid biases of a group of said devices, l andmeans controlled by the passage of current through the device of highestnegative grid bias which has been overcome for preventing the passage ofcurrent through the devices of lower grid bias.

24. In combination, a plurality of gasdischarge devices ofthe triggeraction type having grids, means responsive to current flow in the platecircuit of said devices, means for normally applying dlil'erent negativegrid bias to the respective grids' of said devices, means forovercomingthe negative grid bias of a plurality of saidA devices, andmeans controlled by the current flow in the device of highest negativegrid bias overcome for opening the plate circuit of the devices havinglower grid biases.

25. In combination, a plurality of gas discharge devices of the triggeraction type having grids, slow acting relays for producing a, desiredresponse controlled by current ilow in the plate circuits of saiddevices, means for applying different negative grid bias to therespective grids of said devices, means for overcoming the negative gridbias of a plurality of said devices, 'and fast acting relays controlledby current non in the plate circuits of said devices for opening theplate circuits of the devices having lower grid biases.

26. In combination, means for initiating electrical pulsescorrespondingto intelligible characters, each character beingrepresented by a single pulse of different electrical magnitude fromthose representing other characters, means for conveying said pulses toa remote point, said last mentioned means comprising a cable system andmeans .for controlling the pulse form, a system comprising a pluralityof gas discharge devices of the trigger action type respectivelyresponsive to pulses of different magnitude combined with means forpreventing the operation of more than one device in response to a givenpulse. and means actuated: thereby for indicating the various charactersindicated by the pulses.

MAURICE D. SARBEY.

